1. Field of the Invention
This invention relates to laser fusion welding and more particularly to a hand held powder-fed laser fusion welding torch.
2. Description of the Related Art
In general, the surface of a metallic article may be welded and/or alloyed by the simultaneous and cooperative operation of a laser beam and an alloy powder stream. To accomplish this, systems exist that have a laser source and focusing apparatus, with a powder delivery apparatus provided as part of an integral package. The laser beam melts a relatively small area at the surface of the article, and a controlled volume of alloying particles are delivered into the melt pool via the powder flow stream.
In laser fusion welding, an article of metal or other material may have the surface thereof alloyed, or otherwise treated, by the simultaneous and cooperative operation of a laser beam with an alloy powder. Typically, the laser beam melts a relatively small volume of the outer surface of the article and the powder system delivers a controlled volume of alloying particles into this molten volume. The alloying particles become dispersed throughout this volume and therewith alter, complement, or add to the composition of the outer layer in a controllable way. Removal of the beam, such as by advancement of the workpiece relative to the focal point of the beam, causes the molten volume to be rapidly chilled. The chilling occurs so rapidly that the volume retains the characteristics of the molten mix.
As an example, gas turbine engines, such as those utilized with jet aircraft, are being designed with ever increasing performance requirements. One element of the engine which has been receiving attention is the seal created between the outer periphery of the rapidly rotating blades and the surrounding housing. Another element subject to attention is the turbine nozzle system in jet engines.
The owner of the present invention, Honeywell International, Inc., often repairs turbine nozzles with a process called JetFix. The JetFix process uses steps as follows: chemically and mechanically stripping the outer aluminide coating, welding the cracks, thermally shocking the welds (to form micro cracks), fluoride ion cleaning of the cracks, (to remove oxides), applying a JetFix braze alloy, vacuum furnace brazing, blending brazing, re-application of aluminide coating, and effective flow area check.
Laser powder fusion (LPF) technology has been in use for the past twelve years and has demonstrated the benefits of small heat affected zones on turbine airfoils. Some repair facilities, such as those at Honeywell International Inc., have successfully repaired over 500,000 airfoils which have subsequently accumulated over 10 million flight hours. However, commercially available LPF machines are relatively large and usually run along pre-programmed paths for the repair of a specific part. Thus, one limitation of LPF is the inability of the user to manipulate the laser torch in a custom manner during the repair process as the weld occurs. Accordingly, there is a need for an LPF apparatus that can allow the user to tailor the weld and welding process to the workpiece as the laser is being operated. The present invention satisfies this need.
The present invention provides a hand-held powder-fed laser fusion welding torch that allows customized welding by delivery of laser light onto a stream of welding fusion powder. The ability to provide such a compact laser welding system increases convenience and flexibility, enabling the welder to create or repair objects with greater skill, flexibility, and efficiency.
Worn or damaged metal parts and assemblies may be repaired or dimensionally restored through high power laser processing with a laser source of sufficient intensity to melt so the metal surface while a metallic filler in the form of a powder, wire or rod is introduced into the melt pool. Metallic precursors in a liquid or semi-liquid form may also be applied to the surface, allowed to dry, and then laser processed. In situations where the work surface is not accessible by conventional workstation type of laser powder metal fusion equipment, a compact hand-held torch is preferred. Other cases may involve the repair of parts having irregular and random cracks or damage not otherwise repairable by robotic or programmable workstations. In order to perform repairs of this type, a portable, flexible delivery system is, required for both laser as well as the metal filler. This invention provides for these needs through the integration of laser beam and metal powder delivery components into a single compact hand-held unit. The laser source may be a continuous wave Nd:YAG laser.
In one embodiment, the hand held laser includes a body and a nozzle assembly mounted on the body, with the nozzle assembly defining a central nozzle aperture through which gas and light including laser light may pass. The nozzle defines first and second powder flow channels aligned with a working focal point adjacent the central nozzle aperture. Fusion powder may be transmitted through the first and second powder flow channels for fusing by laser light transmitted through the central nozzle aperture.
In another embodiment, a method is provided to manually laser powder fusion weld a workpiece in order to effect construction and/or repair. A hand held powder-fed laser fusion welding torch is provided that may be manually operated. In such manual operation, the torch generally enjoys significant degrees of spatial freedom so that the welder may dispose the torch in a variety and number of easily-achieved positions. In this way, the welder may conform his activities to the needs at hand and is preferably not limited by physical constraints of the laser torch.